Process for the preparation of derivatives of fatty acids

ABSTRACT

The preparation of a mixture comprising branched fatty acids and oligomerised fatty acids comprises contacting a source of unsaturated fatty acids or their derivatives with an ionic liquid.

The present invention relates to a process for the preparation of amixture of branched and oligomeric fatty acids, by contacting acomposition comprising unsaturated straight chain fatty acids with anionic liquid. Fatty acids are versatile building blocks in various partsof the chemical industry, ranging from lubricants, polymers, solvents tocosmetics and much more. Fatty acids are generally obtained byhydrolysis of triglycerides of vegetable or animal origin. Naturallyoccurring triglycerides are esters of glycerol and generally straightchain, even numbered carboxylic acids, in size ranging from 10-24 carbonatoms. Most common are fatty acids having 12, 14, 16 or 18 carbon atoms.The fatty acids can either be saturated or contain one or moreunsaturated bonds.

Long, straight chain saturated fatty acids (C10:0 and higher) are solidat room temperature, which makes them difficult to process in a numberof applications. The unsaturated long chain fatty acids like e.g. oleicacid are liquid at room temperature, so easy to process, but areunstable because of the existence of a double bond. Derivatives of fattyacids that are branched (i.e. branched fatty acids) mimic the propertiesof the straight chain in many respects, however, they do not have thedisadvantages associated with them. For example branched C18:0(commercially known as isostearic acid) is liquid at room temperature,but is not as unstable as unsaturated C18:1, since the unsaturated bondsare prone to oxidation. Therefore, branched fatty acids are for manyapplications more desirable than straight chain fatty acids.

Apart from branched fatty acids other fatty acid derivatives, such asoligomerised fatty acids, find use in similar and other applications.Oligomeric fatty acids refer to materials prepared by coupling of themonomer units, of which typically dimeric and trimeric species aredesired building blocks in plastics, the personal care industry,lubricants, etcetera.

Mixtures comprising oligomerised fatty acids and branched fatty acidscan be likewise useful.

Currently, branched and oligomeric fatty acids are obtained byisomerisation/oligomerisation of the straight chain, unsaturated fattyacids. The reaction is conventionally carried out using a clay catalyst,and is generally performed at high temperature (e.g. 250° C.). A commonprocess is the preparation of branched C18:0 and dimerised C18 (i.e. C36dicarboxylic acids) from unsaturated straight chain C18:1 (or alsoC18:2). A disadvantage in this conventional process is that substantialamounts of aromatic dimers are formed. Such compounds are undesirablefor a number of reasons, of which the most notable are: they do notcontribute to the properties desired, and they can present a healthhazard. The latter precludes the use of conventional dimer acids forcertain highly desirable applications in the personal product andcosmetics industries.

In addition, the prior art processes suffer from the disadvantage thatalthough a reasonable amount of polymerised product is obtained, theratio of dimerised to trimerised and higher fatty acids is fixed andcannot easily be tuned to market demand.

Hence, there is a need for a process for the preparation of a mixturecomprising branched and oligomeric fatty acids, in which mixture theconcentration of aromatic dimers is low, or preferably substantiallyzero.

It has now been found that the above objectives can be met by a processfor the preparation of a mixture comprising branched fatty acids anddimerised fatty acids, wherein a source comprising unsaturated fattyacids or derivatives thereof, is contacted with an ionic liquid.

An ionic liquid is herein to be understood as a salt (or a mixture ofsalts) in its liquid form (i.e. molten).

Preferably, to lead to the desired products, in the process according tothe invention, the source comprises at least 50% by weight of fattyacids or derivatives thereof, having at least one unsaturatedcarbon-carbon bond in the fatty acid chain. It is also preferred that atleast 50% by weight of said fatty acids or derivatives of fatty acidshave a fatty acid chain length of between 8 and 24 carbon atoms. Apreferred fatty acid in this respect is oleic acid or derivativesthereof.

Regarding the derivatives in the source as mentioned, esters arepreferred, with alkylesters being the most preferred. Of thesealkylesters, the most preferred ones are the fatty acid esters ofalcohols having 1-4 carbon atoms, e.g. methanol, ethanol, propanol.Hence, a preferred source for performing the reaction according to theinvention comprises oleic acid, methyl oleate, and/or ethyl oleate.

With respect to the type of ionic liquid, a wide variety ofpossibilities exists. However, it will be clear that the preferred ionicliquids are the ones that are liquid at relatively low temperatures.Although some salts have very high melting points (i.e. common NaCl hasa melting point of approx. 850° C.), there are salts known which meltunder less severe conditions. An example of such salts are mixtures oftwo or more salts. In the case in which a mixture of two salts is used,the resulting ionic liquid is called a binary ionic liquid. Hence, it ispreferred that in the process as set out above the ionic liquidcomprises a binary ionic liquid.

Preferred binary ionic liquids comprise a metal(III) chloride and/or anorganic halide salt, e.g. [A]⁺X⁻. Also, inorganic halide salts can beused. Suitable metal (III) chlorides include aluminium (III) chlorideand iron (III) chloride. Regarding the organic halide, an unsymmetricalimidazolium or pyridinium halide has the advantage thatisomerisation/oligomerisation may now occur under mild conditions,contrary to conventional processes. A preferred unsymmetricalimidazolium halide is 1-methyl-3-ethyl imidazolium chloride.

A distinct advantage of the presently invented process over the knownprocesses is that there is no need to carry out a reaction for branchingand/or oligomerisation of fatty acids at elevated temperatures: as longas the temperature is high enough for the salt which is used as thereaction “solvent” (or medium) to be in its liquid form (i.e. molten).An additional advantage is that substantially no aromatic and/or cyclicdimers are formed in the process according to the invention.

Therefore, it is preferred that the process according to the inventionis carried out at temperatures below 250° C. More preferred areoperating temperatures of below 150° C., or even below 50° C., as longas the ionic liquid is chosen such that the mixture of ionic liquid andreactants is a liquid. Some reaction systems are even active attemperatures below 0° C. At such temperatures, the amount at crackedproducts obtained can be low, and following this, such a temperature canbe preferred for some cases.

As an additional advantage, there is no need for performing the reactionunder increased pressure, and therefore, it is preferred for thereaction according to the invention to be carried out at atmosphericpressure.

Yet a further advantage of the present process is that long reactiontimes are not needed. Generally, the reaction can be shorter than 60minutes, in many cases even shorter than 15 minutes.

In the process according to the invention, the ratio of ionic liquid:fatty acid reactant is preferably larger than 1:1, preferably at least3:1, and most preferably at least 6:1.

In a practical set up, the process will be preferably be operated in a(semi-) continuous way, and the products are separated from thereactants and ionic liquid. The expensive unsymmetrical imadazolium orpyridinium halide can be easily separated from the product by extractionwith solvents such as dichloromethane and hexane etc, together withmixtures thereof. The imidazolium or pyridinium species can then berecycled following evaporation or distillation of the solvent.

The invention is further illustrated by the following examples, whichare not to be interpreted as limiting the invention thereto.

EXAMPLE 1 Branching/oligomerisation of methyl oleate.

In a dry box, 1-methyl-3-ethylimidazolium chloride (3.55 g, 24.20 mmol)was added to triply sublimed aluminium (III) chloride (6.45 g, 48.40mmol), in a 100 cm³ round bottomed flask, equipped with a dinitrogeninlet, Teflon stirrer bar and a stopper. The two solids were left tostand for 1 h without stirring, at which point the melt had partiallyformed. The melt was transferred to a fume cupboard and connected to asupply of dinitrogen, and cooled to a reaction temperature of 0° C.Methyl oleate (3.56 g, 12.10 mmol, molar ratio of ionic liquid to methyloleate 6:1) was added dropwise by pipette over a 10 minute period, andthe whole system kept under a constant stream of dinitrogen to preventair/moisture entering the reaction. The reaction was allowed to proceedfor 1hr, at which point the reaction mixture was quenched by theaddition of water and crushed ice (50 cm³). The resultant organic phasewas then extracted with 3×30 cm³ aliquots of dichloromethane. Thecombined organic extracts were dried using MgSO₄, filtered, and thesolvent evaporated using a rotary evaporator.

The various products were separated by flash chromatography on 100 g ofsilica, using a gradient elution (500 ml of 2%, followed by 5%, followedby 10% ethyl ethanoate in 40-60° petroleum ether.) Following separationthe products were identified by a combination of ¹H & ¹³C NMR, GCMS andinfra-red.

Selectivities for the various products obtained under these conditionsare presented in Table 1. This table also outlines the results of otherexperiments performed in the same manner as outlined in this example butusing various ionic liquid: methyl oleate ratios, reaction times andreaction temperatures.

Selectivity to branched/oligomeric fatty esters can be tailored todemand by controlling either the reaction rate or the ratio of ionicliquid: fatty acid reactant. Short reaction times and low temperaturesfavouring the production of branched monomer and dimer moieties, longreaction times/high temperatures favouring the production of trimer andhigher polymeric species. Similarly high dilution of the unsaturatedfatty ester feedstocks in the ionic liquid catalyst/solvent systemfavour the production of branched and dimer moieties.

Analysis of the dimer fractions obtained from all these experiments, byNMR, revealed the complete absence of cyclic or aromatic structures.

TABLE 1 Effective of ionic liquid:reactant mole ratio, reactiontemperature and reaction on time on product selectivity Reac. Mol Temp/time % % % % % % rat. ° C. mins BM LM DIM TRIM Poly Crac 3:1 −40 10 26 138 19 <10 0 3:1  0 10 20 1 19 30 <20 5 1.1:1   −40 10 17 1 18 43  20 01.1:1    25 10 25 2 14 32  20 0 (BM = Branched monomer, LM = Linearmonomer, DIM = Dimer, TRIM = trimer, Poly = Polymer, Crac = Crackedproducts) *Note the oligomeric fractions in this experiment were notseparated.

The cracked products observed are sweet smelling volatile low molecularfatty acid esters.

EXAMPLE 2 Effect of reaction temperature

Example 1 has been repeated using the same conditions, except that theionic liquid: fatty acid reactant ratio is now 6:1, and the reaction hasbeen performed at various temperatures (see table 2). All otherconditions remained the same.

TABLE 2 Effect of temperature at a ionic liquid: fatty acid reactantratio = 6:1 % Trimer & higher % Cracked Temperature/° C. % Monomer %Dimer polymers products −40 13.5 .5 80.9 1.1 −10 17.4 3.2 54.6 24.7 018.3 6 49.3 26.4 8 21.1 5.3 50.3 23.3 25 20.5 15.7 43.8 19.9 50 16.1 9.634.6 39.7 60 14 11.4 33.5 41.1 120 11.9 5.8 32.3 50.0

EXAMPLE 3 Effect of water addition

In a dry box, 1-methyl-3-ethylimidazolium chloride (3.55 g, 24.20 mmol)was added to a triply sublimed aluminium (III) chloride (6.45 g, 48.40mmol) in a 100 cm³ round bottomed flask, equipped with a dinitrogeninlet, Teflon stirrer bar and a stopper. The two solids were left tostand for 1 h without stirring (to avoid excessive reaction rate andheat build up) until the melt had partially formed. The melt was thenstirred for 4 h at which point the aluminium (III) chloride had reacted.The melt was then transferred to a fume cupboard to and connected to asupply of dinitrogen. A mixture of methyl oleate (3,50 g, 12.0 mmol, 50mmol %) and water (0.10 g, 0.1 ml) was added dropwise and stirred atroom temperature for 1.5 h. Water and crushed ice (50 cm³) was added andthe product was extracted with dichloromethane (3×30 cm³). The combinedorganic extracts were dried (MgSO₄), filtered and the solvent evaporatedon a rotary evaporator. This gave 3.10 g of a straw coloured oil.

The various products were separated by flash chromatography on 100 g ofsilica, using a gradient elution (500 ml of 2%, followed by 5%, followedby 10% ethyl ethanoate in 40-60° petroleum ether.) Following separationthe products were identified by a combination of ¹H & ¹³C NMR, GCMS andinfra-red.

Selectivities for the various products obtained under these conditionsare listed below:

Cracked products*: 21% Monomer + dimer: 38% Trimer + polymer: 42% *thecracked products comprise mainly branched fatty acids having between 7and 18 carbon atoms. NMR analysis of the dimer fractions reveals theabsence of cyclic or aromatic structures.

EXAMPLE 4 Alternative extraction to preserve 1-methyl-3-ethylimadazoliumchloride

In a dry box, 1-methyl-3-ethylimadazolium chloride (3.55 g, 24.20 mmol)was added to doubly sublimed aluminium (III) chloride (6.45 g, 48.40mmol) in a 100 cm³ round bottomed flask, equipped with a dinitrogeninlet, Teflon stirrer bar and a stopper. The two solids were left tostand for 0.5 hour without stirring (to avoid excessive reaction rateand heat build up) until the melt had partially formed. The melt wasthen stirred for 3 hours until all the aluminium (III) chloride hadreacted. The melt was transferred to a fume cupboard and connected to asupply of dinitrogen. The reaction vessel was cooled to 0° C. with anice bath and methyl oleate (3.0 g, 10.0 mmol, 30w/w %) was addeddropwise over a fifteen minute period. After a further 5 mins,dichloromethane (25 cm³) was added and the product extracted with hexane(3×33 cm³ aliquots). The solvent was evaporated from the combinedorganic extracts to give 3.31 g of the aluminium adduct of the products.A further 0.84 g of adduct was obtained by washing the melt with 3×33cm³ aliquots of 50:50 dichloromethane/hexane, followed by evaporation ofthe solvent. The adducts were destroyed by addition of water (50 ml),extracted with dichloromethane (2×20 ml), dried (MgSO₄), filtered andthe solvent evaporated on a rotary evaporator. This gave a total of 2.37g of colourless oil (79% of starting product-Remainder is accounted forby volatile products produced as a consequence of cracking reactions).The extracts were separated by Kugelrohr distillation at 2 mmHgpressure.

Cracked products*: 21% Monomer: 14% Dimer:  8% Trimer + Polymer: 57%*the cracked products comprise mainly branched fatty acids havingbetween 7 and 18 carbon atoms. Analysis of the dimer fraction by NMRindicates the absence of cyclic or aromatic dimer structures.

EXAMPLE 5 Effect of iron based ionic liquid on fatty acidoligomerisation

Preparation of 58% Iron (III) Chloride

In a dry-box, triply sublimed FeCl₃ (8.96 g, 55.2×10⁻³ mol) was added to1-ethyl-3-methyl imidazolium chloride (5.86 g, 40×10⁻³ mol). The twosolids were left stirring overnight.

Oligomerisation of methyl oleate in 58% FeCl₃-[emim] Cl

In a dry box, 58% FeCl₃-[emim] Cl (14.82, 40×10⁻³ mol) was transferredto a 3-necked 200 ml round-bottomed flask equipped with a dinitrogeninlet, Teflon stirrer bar and stoppers. The melt was transferred to afume cupboard and connected to a supply of dinitrogen. Methyl oleate(3.0 g, 3.4 cm³, 10×10⁻³ mol) was added dropwise over a 10 minute period. The reaction mixture was left stirring overnight. A sample was thenremoved from the reaction mixture and quenched with distilled water. Theproduct was extracted with dichloromethane, dried (MgSO₄) and thesolvent removed on a rotary evaporator. The sample was analysed byproton NMR which indicated that the reaction was complete. The NMR alsoshowed that some chlorination had occurred. Distilled water was added tothe bulk mixture to quench the combined organic extracts were dried(MgSO₄), filtered and the solvent removed on a rotary evaporator.

A sample of the crude product (0.71 g) was separated by fractionaldistillation under vacuum (2.0 mmHg) on a Kugelrohr apparatus. Thisproduced the following yields:

Monomer 0.23 g (32.4%) Dimer 0.06 g (8.5%)  Trimer + polymer 0.28 g(39.4%) Cracked products 0.14 g (19.7%)

Crude Product

¹H NMR (500 MHz/CDCl₃/TMS) (δ/ppm) 0.85-0.89 (d+t, 4H), 1.28-1.29 (m,28H), 1.61 (m, 2H), 2.28-2.33 (t, 2H), 3.66-3.67 (s, 3H), 3.87-3.89 (m,0.3H).

¹³C NMR (75 MHz/CDCl₃/TMS) (δ/ppm) 14.548, 23.103, 25.397, 25.580,26.920, 29.584, 29.674, 29.736, 30.057, 32.002, 32.334, 34.582, 38.959,52.064, 64.787, 174.763

Note that GCMS showed that there was a high proportion (estimated to be50%) of the monomer which had been chlorinated. A breakdown of theproducts detected by GCMS results is given below:

Retention time/s M⁺ Product 544-552 242 C₁₄ Methyl ester 580-591 256 C₁₅Methyl ester 612-631 270 C₁₆ Methyl ester 654-657 284 C₁₇ Methyl ester688-734 298 C₁₈ Methyl ester 766-881 332 Chlorinated C₁₈ Methyl ester

What is claimed is:
 1. Process for the preparation of a mixturecomprising branched fatty acids and oligomerised fatty acids, wherein asource comprising unsaturated fatty acids or derivatives thereof, iscontacted with a salt or mixture of salts in liquid form.
 2. Processaccording to claim 1, characterized in that the source comprises atleast 50% by weight of fatty acids or derivatives thereof, having atleast one unsaturated carbon-carbon bond in the fatty acid chain. 3.Process according to claim 2, characterized in that the fatty acidfeedstock or derivative thereof, comprises of at least 80% by weight ofunsaturated fatty acid or derivatives thereof.
 4. Process according toclaim 1, characterized in that at least 50% by weight of fatty acids orderivatives thereof have a fatty acid chain length of between 10 and 24carbon atoms.
 5. Process according to claim 4, characterized in that thefatty acid feedstock or derivative thereof comprises at least 40% byweight of oleic acid or derivative thereof.
 6. Process according toclaim 5, characterized in that the fatty acid feedstock or derivativethereof comprises of at least 70% by weight of oleic acid.
 7. Processaccording to claim 1, characterized in that the fatty acid derivative isan alkyl ester of a fatty acid.
 8. Process according to claim 7,characterized in that the fatty acid derivative is an ester of fattyacid and an alcohol having 1-4 carbon atoms.
 9. Process according toclaim 1, characterized in that the salt or mixture of salts in liquidform comprises a binary salt.
 10. Process according to claim 1,characterized in that the salt or mixture of salts in liquid formcomprises a metal (III) chloride and/or an organic halide.
 11. Processaccording to claim 10, characterized in that the metal (III) chloride isaluminium (III) or iron (III) chloride.
 12. Process according to claim10, characterised in that the organic halide is an unsymmetricalimidazolium halide or a pyridinium halide.
 13. Process according toclaim 12, characterized in that the unsymmetrical imidazolium halide is1-methyl-3-ethylimidazolium chloride.
 14. Process according to claim 1,characterized in that it is carried out at temperatures below 150° C.15. Process according to any of claim 1, characterized in that thereaction is performed under atmospheric pressure.
 16. Process accordingto claim 1, characterized in that the salt or mixture of salts in liquidform: fatty acid reactant ratio is larger than 1:1.
 17. Processaccording to any of claim 1, characterized in that substantially noaromatic dimers are produced during the reaction.
 18. Process accordingto claim 1 in which the products are separated from the reactants andsalt or mixture of salts in liquid form.
 19. Process according to claim18 in which the imadazolium or pyridinium halide is separated from theproduct/AlCl₃ adduct by extraction with a polar solvent.
 20. Processaccording to claim 18 in which the product is liberated from theproduct/AlCl₃ adduct by hydrolysis in water.
 21. Process according toclaim 1, characterized in that it is carried out at temperatures below50° C.
 22. Process according to claim 1, characterized in that the saltor mixture of salts in liquid form: fatty acid reactant ratio is atleast 3:1.